You might want to actually install the package and try it for yourself.  The tests/intl_sample.html is a good place to start.  If you change the require statement in there from:
			require([ "./Intl", "./IntlShim"], function(Intl,IntlShim) {
to:
			require([ "./IntlShim", "./IntlShim"], function(Intl,IntlShim) {

then you can see how it behaves if native Intl support is there ( i.e. our Intl won't get loaded ).